Ink-jet head

ABSTRACT

A piezoelectric actuator is provided, including a vibration plate, a piezoelectric layer, a plurality of individual electrodes arranged in two arrays, first and second common electrodes which have first and second facing portions facing parts of the individual electrodes and first and second connecting portions connecting the first and second facing portions respectively, and first and second wiring portions which are arranged on the vibration plate and which are connected to the first and second common electrodes respectively via first and second connecting wirings, wherein one of the first connecting wirings connects the first connecting portion and one of the first wiring portion while striding over the second connecting portion.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 12/872,410. The present application claims priorityfrom Japanese Patent Application No. 2009-200744, filed on Aug. 31,2009, the disclosure of which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric actuator, in which apiezoelectric layer is interposed between individual electrodes andcommon electrodes, and a liquid discharge apparatus provided with thesame.

2. Description of the Related Art

A piezoelectric actuator has been hitherto known, including a channelunit, a top plate (vibration plate) which is arranged on an upper end ofthe channel unit, and a piezoelectric layer which is stacked on thevibration plate, wherein individual electrodes facing pressure chambersare arranged on one surface of the piezoelectric layer, and a firstconstant electric potential electrode which faces substantially centralportions of the individual electrodes and a second constant electricpotential electrode which faces both end portions in the transversedirection of the individual electrodes are arranged on the other surfaceof the piezoelectric layer. In the piezoelectric actuator constructed asdescribed above, the portion, of the piezoelectric layer, facing theindividual electrode and the first constant electric potential electrodeand another portion, of the piezoelectric layer, facing the individualelectrode and the second constant electric potential electrode aresimultaneously deformed. Accordingly, the portions, of the piezoelectriclayer and the vibration plate, which face the pressure chambers aredeformed. Accordingly, it is possible to avoid the so-called crosstalkwhich would be otherwise caused such that the deformation of any portionof the piezoelectric layer facing a certain pressure chamber istransmitted to another portion facing another pressure chamber.

Another piezoelectric actuator has been known, including a vibrationplate, a piezoelectric layer which is stacked on an upper surface of thevibration plate, pressure chambers which are aligned in two arrays inone direction on a surface, of the piezoelectric layer, facing thevibration plate, individual electrodes which are arranged at portions ofthe vibration plate facing the pressure chambers, a common electrodewhich is arranged to extend continuously while ranging over theplurality of pressure chambers on the other surface, of thepiezoelectric layer, not facing the vibration plate, a driver IC whichis arranged on the upper surface of the vibration plate, and wiringlines which are led out to the upper surface of the vibration plate andwhich connect the driver IC and the electrodes to one another. In thepiezoelectric actuator constructed as described above, the wiring lines,which are connected to the individual electrodes, are laid out on thesame surface, of the vibration plate, as the surface on which theindividual electrodes are arranged, and the wiring lines are connectedto the driver IC. Therefore, the reliability is enhanced for theconnection between the individual electrodes and the driver IC. In otherwords, the various electrodes such as the individual electrodes and thelike are connected to the driver IC without using any wiring member suchas FPC or the like. Therefore, the reliability is enhanced for theelectrical connection and the physical connection between the electrodesand the driver IC.

SUMMARY OF THE INVENTION

The present inventors have contrived a piezoelectric actuator which hastwo types of common electrodes, wherein wiring lines, which areconnected to various electrodes, are led out to an upper surface of avibration plate, and the wiring lines are connected to a driver IC. Inthe case of the piezoelectric actuator constructed as described above,it is also possible to avoid the crosstalk. Further, the electrodes suchas individual electrodes and the like can be connected to the driver ICwithout using any wiring member such as FPC or the like. Therefore, thereliability is enhance for the physical and electrical connectionbetween the driver IC and the electrodes such as the individualelectrodes and the like.

Further, the present inventors have found out such a possibility thatthe electric potential distribution of a common electrode may benonuniform on account of the following reason in relation to apiezoelectric actuator contrived by the present inventors. Thus, thepresent invention has been achieved.

According to the knowledge of the present inventors, it is preferablethat the electric potential of the common electrode is uniform at allportions in order to uniformize the driving characteristics of theportions corresponding to respective pressure chambers in thepiezoelectric actuator. If the wiring line for applying the electricpotential is connected to the common electrode at only one position, itis feared that the electric potential (first electric potential) of theportion (first portion) of the common electrode connected to the wiringline is not identical with the electric potential (second electricpotential) of the portion (second portion) separated from the terminalportion. According to the knowledge of the present inventors, it isfeared that the second electric potential may be deviated from the firstelectric potential as the distance of electrical connection is moreprolonged between the first portion and the second portion. In view ofthe above, the present inventors have found out the fact that it isnecessary to connect the wiring lines at a plurality of mutuallyseparated positions on the common electrode in order to suppress thenonuniform electric potential.

The two types of common electrodes described above are providedcorresponding to the pressure chambers (individual electrodes) which arearranged in two arrays in one direction. Therefore, at least one of thetwo types of common electrodes has two portions which correspond to theindividual electrodes included in the respective arrays and which arearranged while being separated from each other with the other commonelectrode intervening therebetween in relation to the directionperpendicular to the one direction. Therefore, in order to uniformizethe electric potential between the mutually separated two portions, itis necessary that the portions should be in conduction with each other.

In this case, assume that the common electrode has the portions whichare separated from each other as described above and the commonelectrode has no portion which allows the portions to be in conduction.Then it is possible to connect the wiring lines to the mutuallyseparated portions respectively for the two types of common electrodeson the surface of the piezoelectric layer on which the common electrodeis arranged. However, the present inventors have found out the followingfact. That is, in this case, it is feared that any dispersion(fluctuation) may arise in the electric potential between the mutuallyseparated portions.

An object of the present invention is to provide a piezoelectricactuator which is constructed such that two types of common electrodesretained at mutually different electric potentials are arranged on anidentical surface of a piezoelectric layer and which makes it possibleto uniformize the electric potentials of the two types of commonelectrodes at all portions respectively, and a liquid dischargeapparatus provided with the same.

According to an aspect of the present invention, there is provided apiezoelectric actuator including:

a vibration plate;

a piezoelectric layer which is stacked on the vibration plate;

a plurality of individual electrodes which are arranged on one surfaceof the piezoelectric layer and which form individual electrode arraysarranged in two arrays in one direction;

a first common electrode which is arranged on the other surface of thepiezoelectric layer and which has a plurality of first facing portionseach facing a part of one of the individual electrodes and a firstconnecting portion connecting the first facing portions;

a second common electrode which is arranged on the other surface of thepiezoelectric layer, which is electrically insulated from the firstcommon electrode, and which has a plurality of second facing portionseach facing another part of one of the individual electrodes and asecond connecting portion connecting the second facing portions;

a plurality of first connecting wirings which are connected to the firstcommon electrode, in the first connecting portion at a plurality ofmutually separated positions;

a plurality of first wiring sections which are arranged on the vibrationplate and which are connected to the first common electrode via thefirst connecting wirings;

a plurality of second connecting wirings which are connected to thesecond common electrode, in the second connecting portion at a pluralityof mutually separated positions; and

a plurality of second wiring sections which are arranged on thevibration plate and which are connected to the second common electrodevia the second connecting wirings,

wherein one of the first connecting wirings connects the firstconnecting portion and one of the first wiring sections while stridingover the second common electrode.

Accordingly, the first connecting wiring, which connects the firstconnecting portion and the first wiring portion to one another whilestriding over (stepping over or crossing over) the second connectingportion of the second common electrode, is provided, and thus the firstand second connecting wirings can be connected to the plurality ofmutually separated positions of the first and second common electrodesarranged on the same surface of the piezoelectric layer. It is possibleto uniformize the electric potentials of the first and second commonelectrodes, respectively. The description is made, for example, in thefollowing embodiments for the purpose of convenience assuming that thecommon electrode, which has the facing portions facing the substantiallycentral portions of the individual electrodes, is regarded as the firstcommon electrode, and the common electrode, which has the facingportions facing the portions except for the substantially centralportions of the individual electrodes, is regarded as the second commonelectrode. However, no problem arises even if it is assumed that thecommon electrode, which has the facing portions facing the substantiallycentral portions of the individual electrodes, is regarded as the secondcommon electrode, and the common electrode, which has the facingportions facing the portions except for the substantially centralportions of the individual electrodes, is regarded as the first commonelectrode.

According to the present invention, it is possible to uniformize theelectric potentials of the first common electrode and the second commonelectrode arranged on the same surface of the piezoelectric layerrespectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic arrangement of a printer according to a firstembodiment.

FIG. 2 shows a plan view illustrating an ink-jet head shown in FIG. 1.

FIG. 3 shows a plan view illustrating an upper surface of a vibrationplate shown in FIG. 2.

FIG. 4 shows a plan view illustrating an upper surface of apiezoelectric layer shown in FIG. 2.

FIG. 5 shows a sectional view taken along a line V-V shown in FIG. 2.

FIG. 6 shows a sectional view taken along a line VI-VI shown in FIG. 2.

FIG. 7 shows a view according to a first modified embodimentcorresponding to FIG. 4.

FIG. 8 shows a view according to a second modified embodimentcorresponding to FIG. 6.

FIG. 9 shows a view according to a third modified embodimentcorresponding to FIG. 6.

FIG. 10 shows a view according to a fourth modified embodimentcorresponding to FIG. 4.

FIG. 11 shows a view according to a second embodiment corresponding toFIG. 4.

FIG. 12 shows a view according to a fifth modified embodimentcorresponding to FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A preferred first embodiment of the present teaching will be explainedbelow.

As shown in FIG. 1, a printer 1 includes, for example, a carriage 2, anink-jet head 3, and a transport roller 4. The carriage 2 isreciprocatively movable along a guide shaft 5 which extends in thescanning direction (left-right direction in FIG. 1). The ink-jet head 3is arranged on a lower surface of the carriage 2, and the ink-jet head 3discharges inks from nozzles 15 (see FIG. 2) arranged on the lowersurface thereof. The transport roller 4 (transport mechanism) transportsthe recording paper P in the paper feeding direction (frontwarddirection in FIG. 1) in cooperation with an unillustrated motor.

In the printer 1, the inks are discharged to the recording paper P,which is transported in the paper feeding direction by the transportroller 4, by the ink-jet head 3 which is reciprocatively moved in thescanning direction together with the carriage 2, and thus the printingis performed on the recording paper P. The recording paper P, for whichthe printing has been completed, is transported in the paper feedingdirection by the transport roller 4, and thus the recording paper P isdischarged from the printer 1.

Next, the ink-jet head 3 will be explained. In order to recognize thepositional relationship more comprehensively, a piezoelectric layer 42described later on is depicted by two-dot chain lines in FIG. 3, and athrough-hole 46 a of an insulating layer 46 described later on and aportion of a wiring line 47 e arranged on the upper surface of theinsulating layer 46 are depicted by two-dot chain lines respectively inFIG. 4.

The ink-jet head 3 includes a channel unit 31 which is formed with inkchannels including, for example, pressure chambers 10 and the nozzles15, and a piezoelectric actuator 32 which is arranged on the uppersurface of the channel unit 31 and which applies the pressure to theinks contained in the pressure chambers 10.

As shown in FIGS. 5 and 6, the channel unit 31 is formed by mutuallystacking four plates of a cavity plate 21, a base plate 22, a manifoldplate 23, and a nozzle plate 24. The three plates 21 to 23 except forthe nozzle plate 24, which are included in the four plates 21 to 24, areformed of a metal material such as stainless steel. The nozzle plate 24is formed of a synthetic resin material such as polyimide.Alternatively, the nozzle plate 24 may be also formed of a metalmaterial in the same manner as the other three plates 21 to 23.

A plurality of pressure chambers 10 and an ink supply port 9 (see FIG.2) are arranged in the cavity plate 21. The pressure chambers 10 havesubstantially elliptical shapes in a plan view in which the scanningdirection (left-right direction in FIG. 2) is the longitudinal directionof the elliptical pressure chamber 10, and the pressure chambers 10 arearranged in two arrays in the paper feeding direction (one direction).Substantially circular through-holes 12, 13 are arranged respectively atportions of the base plate 22 opposed to the both end portions of theplurality of pressure chambers 10 in the scanning direction. The inksupply port 9 is formed at a position communicated with a manifoldchannel 11 as described later on.

The manifold plate 23 is formed with the manifold channel 11 whichextends in the paper feeding direction (up-down direction in FIG. 2) sothat the manifold channel 11 is overlapped with substantially halfportions of the pressure chambers 10 in each of the arrays disposed onthe side of the through-holes 12 in the scanning direction. In thisarrangement, the ink is supplied from the ink supply port 9 to themanifold channel 11. Further, the manifold plate 23 is formed withsubstantially circular through-holes 14 at portions overlapped with thethrough-holes 13. The nozzle plate 24 is formed with the nozzles 15 atportions overlapped with the through-holes 14.

In the channel unit 31, the manifold channel 11 is communicated with thepressure chambers 10 via the through-holes 12, and the pressure chambers10 are communicated with the nozzles 15 via the through-holes 13, 14. Inthis way, a plurality of individual ink channels, which range from theoutlets of the manifold channel 11 via the pressure chambers 10 toarrive at the nozzles 15, are formed in the channel unit 31.

The piezoelectric actuator 32 is provided with a vibration plate 41, apiezoelectric layer 42, a plurality of individual electrodes 43, commonelectrodes 44, 45, an insulating layer 46, and a plurality of wiringlines 47.

The vibration plate 41 is arranged on the upper surface of the cavityplate 21 so that the plurality of pressure chambers 10 are coveredtherewith. The vibration plate 41 is formed of, for example, a ceramicsmaterial such as alumina, zirconia, PZT described later on or the likeor a metal material such as stainless steel or the like. However, whenthe vibration plate 41 is formed of the metal material, in order toavoid the conduction between the conductive vibration plate 41 and theindividual electrodes 43 and/or the wiring lines 47 described later on,it is necessary that an insulating layer (not shown), which is formedof, for example, a ceramics material, should be arranged on the uppersurface of the vibration plate 41 and that the individual electrodes 43and the wiring lines 47 should be arranged thereon.

The piezoelectric layer 42 is formed of a piezoelectric material (PZT)containing a main component of lead titanate zirconate as the mixedcrystal of lead titanate and lead zirconate. The piezoelectric layer 42is arranged on the upper surface of the vibration plate. Thepiezoelectric layer 42 extends continuously while ranging over theportions facing the plurality of pressure chambers 10.

The individual electrodes 43 are arranged on the upper surface of thevibration plate 41 (lower surface (one surface) of the piezoelectriclayer 42), corresponding to the pressure chambers 10. The individualelectrodes 43 have substantially elliptical shapes which are slightlylarger than those of the pressure chambers 10 in a plan view, and theindividual electrodes 43 are arranged so that the pressure chambers 10are entirely covered therewith. Accordingly, the individual electrodes43 are arranged in two arrays in the paper feeding direction in the samemanner as the pressure chambers 10. The individual electrodes 43 areconnected to a driver IC 50 as described later on. Any one of theelectric potentials of the ground electric potential and thepredetermined positive electric potential (for example, about 20 V) isselectively applied by the driver IC 50.

The common electrode 44 (first common electrode) is arranged on theupper surface of the piezoelectric layer 42. Further, the commonelectrode 44 is connected to the driver IC 50 as described later on. Thecommon electrode 44 is always retained at the ground electric potentialby the driver IC 50. The common electrode 44 has a plurality of facingportions 44 a (first opposing portions, first facing portion), twoconnecting portions 44 b, and a joining portion 44 c. In thisembodiment, a combination of the two connecting portions 44 b and thejoining portion 44 c corresponds to the first connecting portionaccording to the present teaching.

The facing portions 44 a have substantially elliptical shapes which areone size smaller than those of the pressure chambers 10 as viewed in aplan view, and the facing portions 44 a are arranged so that the facingportions 44 a face substantially central portions (certain portions) ofthe pressure chambers 10 (individual electrodes 43). Accordingly, thefacing portions 44 a are arranged in two arrays in the paper feedingdirection in the same manner as the individual electrodes 43. The twoconnecting portions 44 b extend in the paper feeding direction (onedirection) respectively. The two connecting portions 44 b mutuallyconnect left end portions of the facing portions 44 a constituting theleft array and right end portions of the facing portions 44 aconstituting the right array. The joining portion 44 c extends in thescanning direction. The joining portion 44 c mutually connects upper endportions of the two connecting portions 44 b.

The common electrode 45 (second common electrode) is arranged in an areaon the same upper surface of the piezoelectric layer 42 as the surfaceon which the common electrode 44 is arranged, the area being surroundedby the two connecting portions 44 b and the joining portion 44 c. Thecommon electrode 45 is provided with a plurality of facing portions 45 a(second opposing portions, second facing portions) and a connectingportion 45 b (second connecting portion). The facing portions 45 a arearranged to face outer portions, of the pressure chambers 10, disposedoutside the facing portions of the pressure chambers 10 facing thecommon electrode 44. The connecting portion 45 b is the portion, of thecommon electrode 45, as provided by excluding the facing portions 45 afrom the common electrode 45. The connecting portion 45 b mutuallyconnects the facing portions 45 a.

The common electrode 45 is connected to the driver IC 50 as describedlater on. The common electrode 45 is always retained at the constantpositive electric potential by the driver IC 50.

In this arrangement, the portions of the piezoelectric layer 42described above which are interposed between the individual electrodes43 and the common electrode 44 (facing portions 44 a) and the portionsinterposed between the individual electrodes 43 and the common electrode45 (facing portions 45 a) are polarized in the thickness direction ofthe piezoelectric layer 42.

The insulating layer 46 is formed of an insulative material including,for example, a ceramics material such as alumina, zirconia, PZT or thelike or a synthetic resin material. The insulating layer 46 is arrangedover the substantially entire region of the upper surface of thepiezoelectric layer 42 so that the common electrodes 44, 45 are coveredtherewith. The common electrode 44 and the common electrode 45 arearranged closely to one another on the same upper surface of thepiezoelectric layer 42. Therefore, it is feared that the commonelectrode 44 and the common electrode 45 may be in conduction on accountof the migration caused by the material for forming the electrodes.However, the insulating layer 46 is arranged to cover the commonelectrode 44 and the common electrode 45. Therefore, the occurrence ofthe migration as described above is avoided. Further, when athin-layered insulating layer 46 is used, it is possible to thin thepiezoelectric actuator 32. A substantially circular through-hole 46 a,which is filled with a conductive material, is formed through theinsulating layer 46 at a portion opposed to a right-upward end portionof the common electrode 45 as viewed in FIG. 2.

The plurality of wiring lines 47 include a plurality of wiring lines 47a which are individually connected to the individual electrodes 43, twowiring lines 47 b, 47 c which are connected to the common electrode 44,and two wiring lines 47 d, 47 e which are connected to the commonelectrode 45. First ends of the wiring lines 47 are connected to therespective electrodes 43, 44, 45, and second ends of the wiring lines 47are connected to the driver IC 50 arranged on the vibration plate 41.FIGS. 2 to 4 show portions, of the wiring lines 47, disposed in thevicinity of the connecting portions with respect to the electrodes 43 to45 and other portions disposed in the vicinity of the connectingportions with respect to the driver IC 50. The other portions of thewiring lines 47 are omitted from the illustration.

The wiring lines 47 a to 47 e will be explained in further detail below.The first end of the wiring line 47 a is connected to the end portion ofthe individual electrode 43 disposed on the side opposite to the nozzle15 in the scanning direction. Further, the wiring line 47 a is laid outfrom the concerning portion on the upper surface of the vibration plate41 which is positioned on the same surface as the surface on which theindividual electrode 43 is arranged. The second end of the wiring line47 a is connected to the driver IC 50.

In this arrangement, the wiring lines 47 a, which are providedindividually for the individual electrodes 43, have the largest numberamong the wiring lines 47. However, the wiring lines 47 a are laid outon the same surface as the surface on which the individual electrodes 43are arranged, and the wiring lines 47 a are connected to the driver IC50. Therefore, for example, the disconnection or breaking of the wire ishardly caused, and the reliability of the connection is enhanced.

As shown in FIG. 2, the first ends of the two wiring lines 47 b, 47 care connected to the upper end portions of the left connecting portion44 b and the right connecting portion 44 b, respectively, on the uppersurface of the piezoelectric layer 42. Further, the wiring lines 47 b,47 c are led out, from the connecting portions, to the upper surface ofthe vibration plate 41 via the left and right side surfaces of thepiezoelectric layer 42 as viewed in FIG. 2, respectively. Further, thewiring lines 47 b, 47 c are laid out on the vibration plate 41, and thesecond ends of the wiring lines 47 b, 47 c are connected to the driverIC 50. In this embodiment, the portions of the two wiring lines 47 b, 47c, which are arranged on the upper surface of the vibration plate 41,correspond to the first wiring portions according to the presentteaching, and the portions, which connect the first wiring line portionsand the connecting portions 44 b, correspond to the first connectingwirings according to the present teaching.

The first end of the wiring line 47 d is connected to the lower-left endportion (connecting portion 45 b) of the common electrode 45 as viewedin FIG. 2 on the upper surface of the piezoelectric layer 42. The wiringline 47 d is led out from the connecting portion to the upper surface ofthe vibration plate 41 via the lower side surface of the piezoelectriclayer 42 as viewed in FIG. 2. Further, the wiring line 47 d is laid outon the upper surface of the vibration plate 41, and the second end ofthe wiring line 47 d is connected to the driver IC 50.

The first end of the wiring line 47 e is positioned at the portion ofthe upper surface of the insulating layer 46 (surface disposed on theside opposite to the piezoelectric layer 42) facing the through-hole 46a, and the first end of the wiring line 47 e is connected to theupper-right end portion (connecting portion 45 b) of the commonelectrode 45, as viewed in FIG. 2, via the conductive material chargedinto the through-hole 46 a. The wiring line 47 e extends from theconnecting portion on the upper surface of the insulating layer 46 tothe upper end of the insulating layer 46 in the upward direction asviewed in FIG. 2. In this arrangement, the wiring line 47 e is arrangedon the upper surface of the insulating layer 46 so that the wiring line47 e strides over (steps over) the joining portion 44 c of the commonelectrode 44.

As shown in FIG. 6, the wiring line 47 e is further led out to the uppersurface of the vibration plate 41 via the insulating layer 46 and theside surface of the piezoelectric layer 42. The wiring line 47 e is laidout on the vibration plate 41, and the second end of the wiring line 47e is connected to the driver IC 50.

In this embodiment, the portions of the wiring lines 47 d, 47 e, whichare arranged on the upper surface of the vibration plate 41, correspondto the second wiring portions according to the present teaching. Theportions of the wiring lines 47 d, 47 e, which connect the second wiringportions and the common electrode 45 (connecting portion 45 b),correspond to the second connecting wirings according to the presentteaching. In the first embodiment, as described above, the secondconnecting wiring line extends while striding over the first connectingportion.

In this arrangement, unlike the wiring lines 47 a connected to theindividual electrodes 43, the wiring lines 47 b to 47 e, which areconnected to the common electrodes 44, 45, are led out from theconnecting portions with respect to the respective electrodes to theupper surface of the vibration plate 41 which is positioned at theheight different from that of the connecting portions. That is, thefirst and second connecting wirings, which are connected to the firstand second wiring line portions, are arranged on the surface having theheight (position in relation to the stacking direction of the vibrationplate 41 and the piezoelectric layer 42) different from that of thesurface on which the first and second wiring portions are arranged.Therefore, it is feared that the reliability of the connection may bedeteriorated or lowered as compared with the wiring lines 47 a. However,as described above, the two wiring lines 47 b, 47 c are connected to thecommon electrode 44, and the two wiring lines 47 d, 47 e are connectedto the common electrode 45. Therefore, even if any one of the two wiringlines is discontinued or broken, any fear, in which the electricpotential of the electrode may be greatly fluctuated, is not caused. Anyfear, in which the piezoelectric actuator 32 cannot be driven, is notcaused as well.

When the numbers of the wiring lines connected to the common electrodes44, 45 are further increased, it is also possible to improve thereliability of the connection. Even in this case, the numbers can beincreased with ease as compared with the case in which the number of thewiring lines connected to the respective individual electrodes 43 havingthe large number is further increased.

The method for driving the piezoelectric actuator 32 will now beexplained. In the piezoelectric actuator 32, the plurality of individualelectrodes 43 are previously retained at the ground electric potential.As described above, the constant positive electric potential is appliedto the common electrode 45. Therefore, the electric potential differencearises between the individual electrodes 43 and the common electrode 45(facing portions 45 a). The electric field, which is in the directionparallel to the polarization direction, is generated at the portion(first active portion) of the piezoelectric layer 42 interposed betweenthe electrodes. Accordingly, the concerning portion of the piezoelectriclayer 42 is shrunk in the horizontal direction perpendicular to thedirection of the electric field. As a result, the portions of thevibration plate 41, the piezoelectric layer 42, and the insulating layer46, which face the pressure chambers 10, are deformed as a whole toprotrude toward the opposite side of the pressure chambers 10. Thevolume of the pressure chambers 10 are increased as compared with thestate in which the deformation is not caused.

When the piezoelectric actuator 32 is driven, the electric potential ofany desired individual electrode 43 is switched from the ground electricpotential to the positive electric potential. In this situation, theindividual electrode 43, which has been switched to have the positiveelectric potential, has the electric potential equal to that of thecommon electrode 45. Therefore, the portion of the piezoelectric layer42, which is interposed between the individual electrode 43 and thecommon electrode 45, is returned to the state having been providedbefore the shrinkage. On the other hand, as described above, theelectric potential difference arises between the individual electrode 43and the common electrode 44 (facing portion 44 a), because the groundelectric potential is applied to the common electrode 44. Accordingly,the electric field, which is directed in the direction parallel to thepolarization direction, is generated at the portion (second activeportion) of the piezoelectric layer 42 interposed between the individualelectrode 43 and the common electrode 44 (facing portion 44 a). Theconcerning portion of the piezoelectric layer 42 is shrunk in thehorizontal direction perpendicular to the direction of the electricfield. Accordingly, the portions of the vibration plate 41, thepiezoelectric layer 42, and the insulating layer 46, which are opposedto the corresponding pressure chamber 10, are deformed as a whole toprotrude toward the corresponding pressure chamber 10, and the volume ofthe pressure chamber 10 is decreased. As a result, the pressure of theink contained in the pressure chamber 10 is raised, and the ink isdischarged from the nozzle 15 communicated with the correspondingpressure chamber 10. After the ink discharge, the electric potential ofthe individual electrode 43 is switched from the positive electricpotential to the ground electric potential, and the piezoelectricactuator 32 is returned to the initial state.

In this situation, in the piezoelectric actuator 32, when the electricpotential of the individual electrode 43 is switched from the groundelectric potential to the positive electric potential, the portion ofthe piezoelectric layer 42, which is interposed between the individualelectrode 43 and the facing portion 44 a, is shrunk in the horizontaldirection. Further, simultaneously therewith, the portion of thepiezoelectric layer 42, which is interposed between the individualelectrode 43 and the facing portion 45 a, is elongated from the shrunkstate to the state having been provided before the shrinkage.Accordingly, the influence exerted by the shrinkage of the piezoelectriclayer 42 and the influence exerted by the elongation thereof arecounteracted with each other. As a result, it is possible to avoid theso-called crosstalk which would be otherwise caused such that thedeformation of any portion of the piezoelectric layer 42 facing acertain pressure chamber 10 is transmitted to any other portion facinganother pressure chamber 10.

In order to uniformize, for example, the discharge speed and the volumesof the ink droplets discharged from the respective nozzles 15 when thepiezoelectric actuator 32 is driven, it is necessary that the electricfield, which is generated in the piezoelectric layer 42, should beuniformized. For this purpose, it is necessary that the electricpotentials of the common electrodes 44, 45 should be uniformized at allportions respectively. It is hypothetically assumed that one contact isprovided between each of the wiring lines 47 and each of the commonelectrodes 44, 45. In this case, it is difficult to uniformize theelectric potentials at all portions of the common electrodes 44, 45respectively, because the common electrodes 44, 45 are the relativelylarge electrodes which are provided to range over the plurality ofpressure chambers 10 (individual electrodes 43). That is, the electricpotentials of the common electrodes 44, 45 are not uniform in all areas.As the portions of the common electrodes 44, 45 are separated fartherfrom the portions of connection with respect to the wiring lines 47, theelectric potentials of the concerning portions are more deviated fromthe electric potentials provided at the contact portions with respect tothe wiring lines 47. Therefore, in order to uniformize the electricpotential, as described above, it is necessary that the wiring lines 47(first and second connecting wirings) should be connected at a pluralityof positions of the common electrodes 44, 45 separated from each other.

As for the common electrode 44, the two connecting portions 44 b arearranged while being separated from each other in the scanningdirection. Therefore, in order to uniformize the electric potential ofthe common electrode 44, it is necessary that the two connectingportions 44 b should be connected to one another.

However, it is difficult that, on the upper surface of the piezoelectriclayer 42, all of the wiring lines 47, which are connected to theplurality of mutually separated portions of the common electrodes 44,45, are connected to the common electrodes 44, 45, and that, on theupper surface of the piezoelectric layer 42, the two connecting portions44 b are connected to one another.

This situation will be explained specifically below. When the commonelectrode 44 has the joining portion 44 c, and the two connectingportions 44 b are connected to one another by the joining portion 44 con the upper surface of the piezoelectric layer 42 as in thisembodiment, then the electric potential is uniformized for the twoconnecting portions 44 b. However, in this case, the common electrode 45is surrounded on the three sides by the two connecting portions 44 b andthe joining portion 44 c. Therefore, if the situation holds as it is, itis inevitable that the wiring line 47 d, which is connected to thecommon electrode 45, should be connected to only the lower end portionof the common electrode 45. In this case, it is feared that the electricpotential provided at the upper end portion of the common electrode 45separated from the connecting portion with respect to the wiring line 47and the electric potential provided in the area near to the connectingportion with respect to the wiring line 47 d may be nonuniform.

On the other hand, if the joining portion 44 c is removed from thecommon electrode 44, then the wiring lines 47 can be connected to theupper end portion and the lower end portion of the common electrode 45(connecting portion 45 b) on the upper surface of the piezoelectriclayer 42, and hence it is possible to uniformize the electric potentialof the common electrode 45. However, in this case, the two connectingportions 44 b are not connected to one another. Therefore, it is fearedthat any dispersion may arise in the electric potential between the twoconnecting portions 44 b.

On the contrary, in this embodiment, as described above, the twoconnecting portions 44 b of the common electrode 44 are connected by thejoining portion 44 c, and the wiring line 47 d is connected to the lowerend portion of the connecting portion 45 b of the common electrode 45.Further, the wiring line 47 e (second connecting wiring), which extendson the upper surface of the insulating layer 46 while striding over thejoining portion 44 c, is connected to the upper end portion of theconnecting portion 45 b. Therefore, it is possible to uniformize theelectric potentials of the common electrodes 44, 45 respectively.

Further, the wiring line 47 e, which is connected to the commonelectrode 45 while striding over the joining portion 44 c, is arrangedon the upper surface of the insulating layer 46 which covers the commonelectrodes 44, 45 therewith. Therefore, it is possible to prevent thewiring line 47 c from any conduction with the joining portion 44 c. Theportion of the common electrode 45 to which the wiring line 47 e isconnected and the portion to which the wiring line 47 d is connected areformed at the positions (positions substantially in point symmetry withrespect to the center of the common electrode 45) separated from eachother in the diagonal line direction of the substantially rectangularcommon electrode 45, in order to secure the distance between theseportions. In this way, in order to uniformize the electric potentialdistribution of the common electrode as uniformly as possible, it isdesirable that the wiring lines, which supply the electric potential tothe common electrode, are connected to the common electrode at thepositions which are separated from each other as far as possible.

Next, modified embodiments, in which various modifications are appliedto the first embodiment, will be explained. However, the components orparts, which are constructed in the same manner as those of theembodiment of the present teaching, are designated by the same referencenumerals, any explanation of which will be appropriately omitted.

In a first modified embodiment, as shown in FIG. 7, the common electrode44 further includes a joining portion 44 d which connects the lower endportions of the two connecting portions 44 b. Accordingly, the commonelectrode 45 is surrounded on the four sides by the two connectingportions 44 b and the two joining portions 44 c, 44 d.

A wiring line 47 f is provided in place of the wiring line 47 d. Thefirst end of the wiring line 47 f is connected to the lower-left endportion of the common electrode 45 via the conductive material chargedinto the through-hole 46 a formed at the lower-left end portion of theinsulating layer 46 opposed to the common electrode 45. The wiring line47 f extends downwardly from the connecting portion on the upper surfaceof the insulating layer 46 (see FIG. 5) while striding over (steppingover) the joining portion 44 d.

When the common electrode 45 is surrounded on the four sides by the twoconnecting portions 44 b and the two joining portions 44 c, 44 d, thewiring lines cannot be connected to the common electrode 45 on the uppersurface of the piezoelectric layer 42. Even in such a situation, thewiring lines 47 e, 47 f, which extend while striding over the joiningportions 44 c, 44 d, are provided as the wiring lines which areconnected to the common electrode 45. Accordingly, it is possible toconnect the wiring lines to the mutually separated portions of thecommon electrode 45, and it is possible to uniformize the electricpotential of the common electrode 45.

In this case, the lower end portions of the two connecting portions 44 bare connected to one another by the joining portion 44 d in addition tothe fact that the upper end portions of the two connecting portions 44 bare connected to one another by the joining portion 44 c. Therefore, theelectric potential of the common electrode 44 is further uniformized.

In the first embodiment, the portion of the wiring line 47 e (secondconnecting wiring), which extends while striding over the joiningportion 44 c, is arranged on the upper surface of the insulating layer46 which is arranged on the upper surface of the piezoelectric layer 42so that the entire common electrodes 44, 45 are covered therewith.However, the present teaching is not limited thereto. It is notnecessarily indispensable that the insulating layer is formed to coverthe entire common electrode.

In a second modified embodiment, as shown in FIG. 8, an insulating layer81 is arranged on the upper surface of the piezoelectric layer 42 sothat only the joining portion 44 c is covered therewith. The portion ofthe wiring line 47 e, which extends while striding over the joiningportion 44 c, is arranged on the upper surface of the insulating layer81. Further, another insulating layer 82 is arranged on the uppersurface of the piezoelectric layer 42 on which the insulating layer 81and the abovementioned portion of the wiring line 47 e are arranged sothat the common electrodes 44, 45 are covered therewith. The commonelectrode 44 and the common electrode 45 are prevented from anyconduction on the upper surface of the piezoelectric layer 42 owing tothe insulating layer 82.

Also in this case, it is possible to avoid any conduction between thewiring line 47 e and the joining portion 44 c by means of the insulatinglayer 81.

In a third modified embodiment, the conductive material is not chargedinto the through-hole 46 a of the insulating layer 46. As shown in FIG.9, a first end of a wire bonding line 91 is connected to a portion(connecting portion 45 b) of the common electrode 45 exposed from thethrough-hole 46 a, and a second end of the wire bonding line 91 isconnected to a wiring line 47 g arranged on the upper surface of thevibration plate 41. Accordingly, the common electrode 45 and the wiringline 47 g are connected to one another by the wire bonding line 91.Further, in order to avoid any exfoliation of the wire bonding line 91,an insulating material 92, which is composed of, for example, asynthetic resin material and which is formed by the potting, is arrangedto cover not only the wire bonding line 91, but also the connectingportions with respect to the common electrode 45 and the wiring line 47g. In this case, the wiring line 47 g corresponds to the second wiringportion according to the present teaching, and the wire bonding line 91corresponds to the second connecting wiring according to the presentteaching.

In this arrangement, the wire bonding line 91 and the common electrode45 are connected to one another and the wire bonding line 91 and thewiring line 47 g are connected to one another, for example, by means ofthe ultrasonic welding. In this case, the first end and the second endof the wire bonding line 91 are pressed against the foregoing portion ofthe common electrode 45 and the wiring line 47 g respectively (byapplying the pressure) to effect the abutment. In this state, theultrasonic wave is applied to the abutment portions. Accordingly, theportions of the wire bonding line 91 and the common electrode 45 (theportions of the wire bonding line 91 and the wiring line 47 g), at whichthey mutually make the abutment, are converted into the alloy, and thewire bonding line 91 and the common electrode 45 (the wire bonding line91 and the wiring line 47 g) are connected to one another.

Also in this case, the portion of the common electrode 45, which issurrounded by the connecting portions 44 b (see FIG. 4) and the joiningportion 44 c, can be connected to the wiring line 47 g by means of thewire bonding line 91. Therefore, it is possible to uniformize theelectric potential of the common electrode 45 in the same manner as inthe first embodiment.

When the insulating material 92 is formed by means of the potting, theinsulating material 92 also flows into the portion disposed on the lowerside of the wire bonding line 91. Therefore, the portion of theinsulating layer 46, which covers the joining portion 44 c, may beomitted. Further, the wire bonding line 91 is arranged in the state ofbeing separated from the joining portion 44 c. Therefore, it is notnecessarily indispensable to form the insulating material 92.

In the first embodiment and the first to third modified embodiments, thewiring lines 47 e, 47 f, 47 g and the wire bonding line 91 are allowedto stride over the joining portions 44 c, 44 d. However, they may beallowed to stride over any one of the two connecting portions 44 b.

In the first embodiment, the common electrode 44 (first commonelectrode) has the two connecting portions 44 b which are providedcorresponding to the individual electrodes 43 arranged in the two arraysand the joining portion 44 c which connects the two connecting portions44 b, and the common electrode 45 (second common electrode) issurrounded by the two connecting portions 44 b and the joining portion44 c. However, the present teaching is not limited thereto.

In a fourth modified embodiment, as shown in FIG. 10, common electrodes74, 75 are arranged on the upper surface of the piezoelectric layer 42in place of the common electrodes 44, 45. The common electrode 74 (firstcommon electrode) has a plurality of facing portions 74 a (first facingportions) which face the plurality of pressure chambers 10 respectivelyand a connecting portion 74 b (first connecting portion) which mutuallyconnects the plurality of facing portions 74 a.

The common electrode 75 (second common electrode) is arranged tosurround the common electrode 74. The common electrode 75 has aplurality of facing portions 75 a (second facing portions) which facethe plurality of pressure chambers 10 respectively and a connectingportion 75 b (second connecting portion) which mutually connects theplurality of facing portions 75 a.

Wiring lines 47 h, 47 i are connected to an upper end portion and alower end portion of the connecting portion 74 b of the common electrode74 respectively. Wiring lines 47 j, 47 k are connected to an upper-rightend portion and a lower-left end portion (connecting portions 75 b) ofthe common electrode 75 respectively as viewed in FIG. 10.

The first ends of the wiring lines 47 h, 47 i are connected to the upperend portion and the lower end portion of the connecting portion 74 b,respectively, via the conductive material charged into through-holes 46c, 46 d which are formed at portions of the insulating layer 46, (seeFIG. 5) facing the upper end portion and the lower end portion of theconnecting portion 74 b. The wiring line 47 h extends, from theconnecting portion in the upward direction as viewed in FIG. 10, on theupper surface of the insulating layer 46 to stride over the commonelectrode 75 (connecting portion). Further, the wiring line 47 h is ledout to the upper surface of the vibration plate 41 via the upper sidesurface of the insulating layer 46. Similarly, the wiring line 47 i alsoextends, from the connecting portion in the leftward direction, on theupper surface of the insulating layer 46 to stride over the commonelectrode 75 (connecting portion). Further, the wiring line 47 i is ledout to the upper surface of the vibration plate 41 via the left sidesurface of the insulating layer 46.

As described above, the first ends of the wiring lines 47 j, 47 k areconnected to the portions of the common electrode 75, respectively, onthe upper surface of the piezoelectric layer 42. Further, the wiringlines 47 j, 47 k are led out to the upper surface of the vibration plate41 via the right and lower side surfaces of the piezoelectric layer 42as viewed in FIG. 10.

The wiring lines 47 h to 47 k, which are led out to the upper surface ofthe vibration plate 41, are laid out on the upper surface of thevibration plate 41, and the second ends of the wiring lines 47 h to 47 kare connected to the driver IC 50, in the same manner as described inthe first embodiment.

In the fourth modified embodiment, the portions of the wiring lines 47h, 47 i, which are arranged on the upper surface of the vibration plate41, correspond to the first wiring portions according to the presentteaching. The portions of the wiring lines 47 h, 47 i, which arearranged to stride over the common electrode 75 and which connect thefirst wiring portions and the upper/lower end portion of the connectingportion 74 b, correspond to the first connecting wirings according tothe present teaching. The portions of the wiring lines 47 j, 47 k, whichare arranged on the upper surface of the vibration plate 41, correspondto the second wiring portions according to the present teaching. Theportions of the wiring lines 47 j, 47 k, which are allowed to pas alongthe side surfaces of the piezoelectric layer 42 to connect the secondwiring portions and the common electrode 45, correspond to the secondconnecting wirings according to the present teaching. In the fourthmodified embodiment, as described above, the first connecting wiringsextend while striding over the second connecting portion.

Also in this case, the wiring lines 47 h to 47 k are connected to themutually separated portions of the common electrodes 74, 75. Therefore,it is possible to uniformize the electric potentials of the commonelectrodes 74, 75 respectively.

Second Embodiment

Next, a second embodiment of the present invention will be explained.However, in the second embodiment, only a part of the arrangement of thepiezoelectric actuator is different from that of the first embodiment.Therefore, only portions, which are different from those of the firstembodiment, will be explained below.

As shown in FIG. 11, in the second embodiment, the common electrode 44does not have the connecting portion 44 c (see FIG. 4) on thepiezoelectric layer 42. The two connecting portions 44 b are arrangedwhile being separated from each other with the common electrode 45intervening therebetween in the scanning direction (left-right directionas shown in FIG. 11). A wiring line 47 l is connected to the commonelectrode 45 in place of the wiring line 47 e (see FIG. 4).

As shown in FIG. 11, the first end of the wiring line 47 l is connectedto an upper-right end portion (connecting portion 45 b) of the commonelectrode 45 on the upper surface of the piezoelectric layer 42.Further, the wiring line 47 l is led out to the upper surface of thevibration plate 41 (surface disposed on the side opposite to the channelunit) via the upper side surface of the piezoelectric layer 42. Further,the wiring line 47 l is laid out on the upper surface of the vibrationplate 41, and the wiring line 47 l is connected to the driver IC 50. Theportion of the wiring line 47 l, which is arranged on the upper surfaceof the vibration plate 41, corresponds to the first wiring portionaccording to the present teaching. The portion of the wiring line 47 l,which is allowed to pass along the side surface of the piezoelectriclayer 42 to connect the first wiring portion and the common electrode45, corresponds to the first connecting wiring according to the presentteaching.

A bypass wiring 101 is arranged on the upper surface of the insulatinglayer 46 (see FIG. 5). The bypass wiring 101 extends in the scanningdirection while striding over the common electrode 45. The both endsthereof are connected to upper end portions of the two connectingportions 44 b respectively via the conductive material charged intothrough-holes 46 e, 46 f formed at portions of the insulating layer 46facing the upper end portions of the two connecting portions 44 b.Accordingly, the two connecting portions 44 b are connected to oneanother by the bypass wiring 101.

Also in this case, the wiring lines 47 d, 47 l (second connectingwiring) are connected respectively to the mutually separated lower-leftand upper-right end portions (a plurality of portions) of the commonelectrode 45 on the upper surface of the piezoelectric layer 42, in thesame manner as in the first embodiment. Therefore, it is possible toimprove the uniformity of the electric potential of the common electrode45.

Further, the two connecting portions 44 b, which are arranged whilebeing separated from each other with the common electrode 45 interveningtherebetween in the scanning direction, are connected to one another bythe bypass wiring 101 which extends while striding over the commonelectrode 45. Therefore, the electric potential of the common electrode44 is uniformized.

Next, a modified embodiment, in which various modifications are appliedto the second embodiment, will be explained. However, the components orparts, which are constructed in the same manner as those of the secondembodiment, are designated by the same reference numerals, anyexplanation of which will be appropriately omitted.

In the second embodiment, the two connecting portions 44 b, which arearranged and separated from each other, are connected to one another bythe bypass wiring 101. However, the present teaching is not limitedthereto.

In a fifth modified embodiment, as shown in FIG. 12, the commonelectrode 44 further includes a joining portion 44 f which connectssubstantially central portions of the two connecting portions 44 to oneanother. Therefore, the connecting portion 45 b of the common electrode45 is divided into two portions which are separated from each otherwhile interposing the joining portion 44 f in relation to the up-downdirection as viewed in FIG. 12.

In this arrangement, conversely to the second embodiment, the commonelectrode 45 corresponds to the first common electrode according to thepresent teaching, and the common electrode 44 corresponds to the secondcommon electrode according to the present teaching. The respectiveportions of the connecting portion 45 b, which are divided into two,correspond to the first connecting portions according to the presentteaching respectively. That is, the common electrode 45 has the twofirst connecting portions.

In the fifth modified embodiment, the portion corresponding to the firstwiring portion and the portion corresponding to the second wiringportion are reversed to one another, and the portion corresponding tothe first connecting wiring and the portion corresponding to the secondconnecting wiring are reversed to one another, as compared with thesecond embodiment.

Further, a bypass wiring 102 is arranged on the upper surface of theinsulating layer 46 (see FIG. 5). The bypass wiring 102 extends in adirection slightly inclined with respect to the paper feeding direction(left-right direction as viewed in FIG. 12) while striding over thejoining portion 44 f. The both ends of the bypass wiring 102 areconnected respectively to the abovementioned two portions of theconnecting portion 45 b via the conductive material charged into twothrough-holes 46 g, 46 h formed respectively at portions of theinsulating layer 46 facing the two portions of the common electrode 45.Accordingly, the two portions of the connecting portion 45 b areconnected to one another by the bypass wiring 102.

Also in this case, it is possible to uniformize the electric potentialsof the common electrodes 44, 45 respectively at all portions.

Also in the second embodiment, the two connecting portions 44 b may beconnected to one another by means of a wire bonding provided in the samemanner as in the third modified embodiment described above, in place ofthe bypass wiring 101 arranged on the upper surface of the insulatinglayer 46.

In the second embodiment, the bypass wiring 101 mutually connects theupper end portions of the two connecting portions 44 b. However, thebypass wiring 101 may connect other portions of the two connectingportions 44 b. Further, a plurality of bypass wirings may be provided.

In the second embodiment, the common electrode 44 (first commonelectrode) is provided with the two connecting portions 44 b (firstconnecting portions) corresponding to the arrays of the individualelectrodes 43. However, the present teaching is not limited thereto. Itis not necessarily indispensable that the first connecting portionshould be provided corresponding to the array of the individualelectrode 43, provided that the first connecting portion connects atleast two first facing portions to one another. The number of the firstconnecting portions is not limited to two as well. The first commonelectrode may have three or more first connecting portions. When thethree or more first connecting portions are provided, for example, aplurality of bypass wirings are provided to connect every mutuallydifferent two of the three or more first connecting portions. In thisway, it is possible to allow all of the first connecting portions to bein conduction.

In the first and second embodiments described above, the plurality ofindividual electrodes 43 are arranged on the lower surface of thepiezoelectric layer 42, and the common electrodes 44, 45 are arranged onthe upper surface of the piezoelectric layer 42. However, conversely tothe above, the common electrodes 44, 45 may be arranged on the lowersurface of the piezoelectric layer 42, and the plurality of individualelectrodes 43 may be arranged on the upper surface of the piezoelectriclayer 42.

In this case, for example, an insulating layer is arranged between thepiezoelectric layer 42 and the vibration plate 41. The portions of thewiring lines 47 e, 47 f, 47 h, 47 i which extend while striding over thejoining portions 44 c, 44 d and the common electrode 75 (first andsecond connecting wirings) and the bypass wiring 101 are arranged on thelower surface of the insulating layer.

In the first and second embodiments, the common electrode 44 (facingportion 44 a) faces the substantially central portion of the pressurechamber 10, and the common electrode 45 (facing portion 45 a) is opposedto the portion other than the substantially central portion of thepressure chamber 10. However, there is no limitation thereto. Forexample, conversely to the above, the facing portions of the first andsecond common electrodes may face portions of the pressure chamber 10different from those in the first embodiment. That is, the second facingportion may face the substantially central portion of the pressurechamber 10 and the first facing portion may face the portion other thanthe substantially central portion of the pressure chamber 10. In thiscase, for example, the positions and the shapes of the connectingportions of the respective common electrodes may be appropriatelychanged in conformity with, for example, the positions and the shapes ofthe facing portions of the first and second common electrodes.

In the foregoing embodiments, the piezoelectric actuator is arrangedwith only any one of the wiring line which is connected to one of thetwo types of the common electrodes while striding over the other commonelectrode and which is exemplified by the wiring lines 47 e, 47 f, 47 h,47 i and the wire bonding line 91. Alternatively, the piezoelectricactuator is arranged with the bypass wiring which mutually connects thetwo or more connecting portions of one of the two types of the commonelectrodes while striding over the other common electrode and which isexemplified by the bypass wirings 101, 102. However, the piezoelectricactuator may be arranged with both of the two types of the wiring linesdepending on the arrangement of the two types of the common electrodes.

In the foregoing embodiments, the wiring lines 47 e, 47 f, 47 h, 47 iare arranged on the insulating layer, or the insulating material isarranged around the wire bonding line 91 by means of the potting.However, there is no limitation thereto. The wiring lines 47, the wirebonding line 91, and the bypass wiring lines 101, 102 may be formed withcoated electric wires or electric cables.

The foregoing embodiments are illustrative of the exemplary case inwhich the present teaching is applied to the piezoelectric actuator tobe used for the ink-jet head of the so-called serial type printer fordischarging the inks from the nozzles while being reciprocatively movedin the scanning direction together with the carriage. However, there isno limitation thereto. It is also allowable to apply the presentteaching to a piezoelectric actuator to be used for a so-called linehead which is fixed to the printer and which extends over the entirelength in the widthwise direction of the recording paper. Further, it isalso possible to apply the present teaching to a piezoelectric actuatorto be used for any apparatus or device other than the ink-jet head. Thepiezoelectric actuator according to the present teaching is alsopreferably applicable to any liquid discharge head to be carried on aliquid discharge apparatus usable, for example, for an apparatus forproducing a color filter of a liquid display apparatus by dischargingany liquid other than the ink including, for example, a coloring liquidand an apparatus for forming electrical wiring lines by discharging aconductive liquid.

What is claimed is:
 1. An ink-jet head comprising: a channel unitincluding a plurality of pressure chambers communicating with aplurality of nozzles configured to eject liquid droplets; an insulatinglayer disposed on a first surface of the channel unit; a plurality ofindividual electrodes arranged on a second surface of the insulatinglayer, the second surface facing away from the channel unit; apiezoelectric layer that covers the plurality of individual electrodes,the piezoelectric layer being opposite to the channel unit relative tothe plurality of individual electrodes; a common electrode disposed on athird surface of the piezoelectric layer, the third surface facing awayfrom the channel unit; a first wiring line that connects with the commonelectrode; and, a second wiring line that connects with the commonelectrode, wherein the first wiring line and the second wiring line areled out from the third surface of the piezoelectric layer to the secondsurface of the insulating layer via a side surface of the piezoelectriclayer.
 2. The ink-jet head according to claim 1, wherein the channelunit includes the plurality of pressure chambers arranged in a firstdirection, wherein the piezoelectric layer covers the plurality ofpressure chambers arranged in the first direction, and wherein the firstwiring line and the second wiring line are led out from a portion of thethird surface of the piezoelectric layer at a vicinity of an end portionof the piezoelectric layer, and the end portion is positioned at atleast one of one end and the other end of the piezoelectric layer in thefirst direction.
 3. The ink-jet head according to claim 1, wherein thechannel unit includes a first array of ones of the plurality of pressurechambers arranged in a first direction and a second array of anotherones of the plurality of pressure chambers arranged in the firstdirection, the first array and the second array are next to each otherin a second direction that intersects the first direction, wherein thecommon electrode includes a first portion facing to the first array anda second portion facing to the second array, and wherein the firstportion and the second portion are electrically connected to each otherat a vicinity of an end portion of the first portion and the secondportion, and the end portion is positioned at at least one of one endand the other end of the common electrode in the first direction.
 4. Theink-jet head according to claim 3, wherein the first portion and thesecond portion are electrically connected to each other at both ends ofthe common electrode in the first direction.
 5. The ink-jet headaccording to claim 1, wherein the first wiring line and the secondwiring line are disposed on the third surface of the piezoelectriclayer, the second surface of the insulating layer and the side surfaceof the piezoelectric layer.
 6. The ink-jet head according to claim 1,wherein the insulating layer includes a layer made of zirconia.
 7. Theink-jet head according to claim 1, wherein the insulating layer includesa layer made of ceramic material.